1. Field of the Invention
The present invention relates to a method for linearizing potentiometric sensors which comprises the steps of: insertion in a measurement and/or processing station of a potentiometric sensor provided with a resistive track; application of a defined voltage and/or of a defined current across the resistive track; placement of a number of sensing elements composed of metallic contacts distributed at uniform intervals over the length of the resistive track; acquisition of the individual measured values of the sensing elements and determination of the curve of the resistance of the resistive track; and linearization of the resistance of the resistive track by means of sequential adjustment of the resistance of the resistive track.
2. Description of the Background Art
Potentiometric sensors are frequently used where continuous adjustment of a setpoint value is needed or where a measured value is to be linearly acquired over an angle, for example, in order to sense the motion of a brake lever. Such rotary resistors or potentiometers or potentiometric sensors are known in a design in which metallic contacts are applied to a plastic substrate as conductive traces, between the input and output of which is printed a resistive track on the plastic printed circuit board, for example over an angular range. A wiper, by means of which the variable resistance on the resistive track can be adjusted and tapped, then runs over this resistive track. A wide variety of methods for linearizing the resistance of the resistive track on the printed circuit board have been disclosed.
A potentiometric sensor with a resistance applied over an angular range is known from U.S. Pat. No. 4,032,881. The potentiometric sensor has metallic contact areas at its input and output, between which is applied to a printed circuit board a resistive track extending over approximately 270°. To linearize the curve of the resistance over the circumference of the resistive track, contacts that stand in electrical contact with the resistive track are applied to a carrier at regular circumferential intervals adjacent to the resistive track. In this regard, sensing elements that are applied to the contacts distributed over the circumference determine the curve and the linearity of the resistance over the circumference so that trimming of the linearity can take place. Trimming here takes place by the means that radial notches are introduced in the resistive track by a laser, resulting in an increase in the resistance. By these radial notches, it is possible to linearize the curve of the resistance over the circumference.
Another method for linearizing potentiometric sensors is known from U.S. Pat. No. 3,821,845. Here, linearization takes place by a device equipped with sensing elements distributed over its circumference is brought over and onto the resistive track, so that the curve of the resistance over the resistive track can be sensed at discrete points. Once again, trimming is accomplished by a laser, wherein parallel radial notches are introduced into the resistive track.
A disadvantage of the methods for linearizing potentiometric sensors known from prior art is that inaccurate tapping results in errors in the trimming of the resistive track. In this regard, it can be established as inaccurate sensing that a displacement of the sensing element of as little as 0.2% during placement on the resistive track results in errors or deviations of 2% in the resistance. Such measurement methods and methods for linearization are unsuitable to meet today's stringent requirements in, e.g., the automotive industry, since their tolerance ranges lie outside the requirements demanded by the automotive industry. The above-described potentiometric sensors known from the prior art are thus unsuitable for use in a motor vehicle, for example for sensing the position of a brake pedal.